There are currently numerous radio/wireless and cellular access technologies and standards such as Global System for Mobile Communications/General Packet Radio Service (GSM/GPRS), Wideband Code Division Multiple Access/High Speed Packet Access (WCDMA/HSPA), CDMA-based technologies, wireless fidelity (WiFi), Worldwide Interoperability for Microwave Access (WiMAX) and Long Term Evolution (LTE), to name but a few. These and other technologies and standards have been developed during the last few decades, and it can be expected that the development will continue, for example within 5G. Specifications are developed in organizations such as 3rd Generation Partnership Project (3GPP), 3GPP2 and the Institute of Electrical and Electronics Engineers (IEEE).
One important aspect of cellular systems is mobility and handover (HO). Typically, handover in cellular systems is network controlled, where the network is assisted by measurements provided by a UE. Various measurement events (or triggers) can be configured by the network, such that the UE reports e.g., when radio conditions change in a particular way. Consequently, it should be possible for the network to make sound decisions on whether a handover of a UE is needed. For example, for a mobile terminal/UE to inform the network about new strong cells that can be used as a potential new serving cell, different measurement events are defined both in LTE and WCDMA/HSPA.
Intra E-UTRAN Handover is used to handover a UE from a serving eNodeB (source eNodeB) to a target eNodeB using X2 when the MME is unchanged.
Handover procedures are well established procedures and are outlined for example in 3GPP specifications.
There are, however, instances where UEs or other network nodes have capabilities or limitations that are not fully standard compliant and therefore established HO procedures are not applicable.